In recent years, increasing cases of deaths caused by viral infections such as SARS (severe acute respiratory syndrome), norovirus, and avian influenza have been reported. The prospect of a pandemic is now posing a worldwide threat due to ever more advanced transportation networks and continuously mutating viruses. The emergence of new influenza viruses is also an urgent issue that requires immediate action. Although the development of antiviral vaccines is one solution to these problems and is now being hurried, vaccines are only effective in preventing infections by specific viruses because of their specificity. Since vaccine production is a process requiring a considerable amount of time, it is often difficult to reserve required amounts of a particular vaccine. Thus, there is a strong demand for antiviral agents that show antiviral activity against a wide range of viruses.
Viruses are divided into those that are encapsulated in a lipid-containing membrane called an envelope and those that are not. Since an envelope is mostly composed of lipid, it can easily be destroyed by treating with ethanol, organic solvents, soap and other disinfectants. For this reason, viruses with an envelope can easily be inactivated by these disinfectants (i.e., reduction or elimination of the ability to infect). To the contrary, viruses without an envelope are considered to be highly resistant to these disinfectants. As used herein, the terms “virus inactivation activity” and “antiviral activity” both refer to the same activity.
To address the above-described issues, inorganic antiviral agents that have a wider spectrum of activity than organic viral agents have been developed. For example, a fabric impregnated with an antimicrobial dye agent and divalent copper ion is reported to have the ability to inactivate influenza virus (Patent Document 1). Also, an antiviral fiber formed of carboxyl-containing fiber impregnated with a copper compound is reported (Patent Document 2). Furthermore, a cold-worked ultrafine copper fiber effective in inactivating avian influenza virus is reported (Patent Document 3). Use of other elements for inactivation of viruses, for example, use of a titanium oxide photocatalyst, is also reported (Patent Documents 4 and 5).